Plaque wall has a nice 17 (maximus) that is easily top-ropable, Dec crag has Little Thor (20), Lemmington (19) is also sweet, in the Organ Pipes, and fairly easy to set up a top-rope. I'm sure there's a shitload more, though, and probably more concentrated in the one place.

Yeah we top-roped many climbs in declaration crag from a 17+ to a couple of 22s. That's the ideal area for it if you ask me cos no one has to lead to set them up at the top. You just climb around the back and you're safely there with convenient anchor points etc...

Other than that you might like to buy a guide book and check out single pitches around the main area.

Another area is also Charity Buttress although there arent to many routes in yor requested grade range on that wall. Hellpite etc are not to far away from here though and these routes can be top roped, just be cautious using those routes as the top rope setup can be slightly dicey due to some fragile rock etc (Hellspite area)

The top of Mari (*** 17) is fairly easy to get to, but at 40m (from memory) you will not have enough rope to reach the bottom twice (and would not want to belay on such a long rope due to stretch).
The Plaque area is the classic toproping venue. Check out Fang buttress as well.
Otherwise Mitre Rock (disclaimer: I've never climbed there!)
- Steve

Colloseum wall has got an 18 (hard) and two 20/1s (one easyish on top rope) close together. Right around the corner from them there is the hardest grade 16 in the world but it might be ok to top rope. Just over from them there is a grade 15 crack which is quite nice.

That'd be Castration wouldn't it. It's not really that hard you just need to be a) strong and b) probably climbing 5 grades harder in order to make it feel easy. You're right though it's pretty stiff at the grade I reckon, but so is everything else out that way.

Crucifixion is the 16 crack a few metres around the arete left of Christian Crack which is what it sounds like you're talking about. Just cause its got a bit of burly thrutching doesn't mean its harder than 16... :))

In fact the cracks at Colosseum Wall are all spot on for the grade if you can jam.